1. Field
The following description relates to a technology of wireless sensor communication, and, more particularly, to an apparatus and method for stopping data transmission when a coordinator, which is a superordinate layer of a sensor device, is in an orphaned state, thereby reducing unnecessary power consumption of the sensor device.
2. Description of the Related Art
IEEE 802.15.4, which is a standard protocol for low-power and low-rate wireless personal area networks (LR-WPANs), specifies a physical (PHY) layer and media access control (MAC) layer for the LR-WPANs. IEEE 802.15.4 is merely a packet data protocol for simple wireless networks, and supports a data rate of 250 kbp/s and star or peer-to-peer networks. In addition, IEEE 802.15.4 supports CSMA/CA algorithm for channel access and 64-bit identifiers/16-bit identifiers.
In a wireless sensor network based on the IEEE 802.15.4 standard, a Personal Area Network (PAN) coordinator is in charge of the whole network which is formed by connecting a plurality of sensor devices or coordinators. A coordinator may be a plurality of sensor devices or a plurality of different coordinators.
A sensor device transmits sensing data, that is, data, through an intermediate coordinator to a PAN coordinator, that is, a final destination. The sensor data periodically transmits data to the coordinator, and receives acknowledgement from the coordinator in response to the receipt of the data. In the case where the coordinator does not receive acknowledgement from the PAN coordinator after transmission of data, the coordinator determines itself to be in an orphaned state, and thus, performs an orphan scan. Regardless whether the orphan scan is performed between the coordinator and the PAN coordinator, the sensor device keeps transmitting data to the coordinator, because the sensor device is not informed of anything about the orphan scan. During the orphan scan, the coordinator receives data in a PHY layer thereof, but throws out the received data. Thus, the coordinator does not transmit acknowledgement to the sensor data in response to the data transmitted from the sensor device. The sensor device retransmits the data to the coordinator for up to a maximum number of retransmission attempts, and if it eventually fails to receive the acknowledgment, the sensor device stops transmitting data.
In such a case, powers are unnecessarily wasted as the sensor device retransmits the data to the coordinator for up to a maximum number of retransmission attempts. In addition, powers are unnecessarily wasted as the coordinator received the data in the PHY layer thereof.